Advanced hot-gas control systems are being designed and tested with operating temperatures in excess of 3000° F. These operating temperatures preclude the use of many metals in the construction of the control systems. Rhenium (“Re”), however, has a melting point of about 3180° C. (5756° F.), and could therefore be used in structural applications at temperatures up to about 2000° C. (3632° F.), and when combined with iridium (“Ir”), at temperature up to about 2200° C. (3992° F.). Moreover, rhenium is chemically compatible with most solid propellants, (i.e., it does not oxidize or carburize in the presence thereof), and it can be coated to prevent these undesirable effects in liquid or gel propellant gases.
Rhenium components are, however, difficult to produce using metallurgical processes such as casting, forming, machining, and joining. Because of rhenium's high melting point, casting is impractical, and therefore powder metallurgy is the primary processes for producing rhenium plate or barstock. This process is labor intensive, expensive, and has a long lead time, as components made via powder metallurgy must go through multiple processing steps and heat treatments, followed by costly and laborious machining processes that require special equipment.
Additional drawbacks to using rhenium include its strong propensity for work hardening, which complicates the use of standard metal working processes that require significant levels of deformation. Joining for the most part is limited to electron beam welding and diffusion bonding.